I used midi sync for Mattomat, should just trigger it playing rather than Mattomat slaving to cubase and use its own clock. And when the midi sync works it's nice to sync filter modulation and stuff at the correct bpm straight away using timing options rather than the rate knob. Not using cubase midi clock makes everything a lot more stable though.

But the midi clock is useful if you plan to change bpm during playing with the daw, no ? If your track has a fixed bpm, you just need to set all sync devices to the right bpm value.
Sure : if you want to change the bpm, you'll have to change all those devices settings ! But I've noticed that sometimes, to set a delay, for instance, to a little bit different bpm value can have excellent, even better results : for a 120bpm track, set a delay at 118bpm, it gives a little swing, sometimes. (just an example)

Yes I hope all the older Cubase will work - VST 5.1 / SX / 4 / 6 / 8 / 9 - VST 5.2 I still have this baby - - The score version - and as a bonus on the EMU 1812 M or whatever Cubase VST 5 ordinaire was included - One of the EMU's will reside on the Xite computer - Just right -